The present invention relates to a model-based method of estimating the crankcase oil temperature of an internal combustion engine.
Crankcase oil is utilized in internal combustion engines for both lubrication and cooling, and an accurate indication of the oil temperature is useful for control purposes such as estimating the viscous friction of the engine and the response time of oil-activated actuators. Although the oil temperature may be measured directly with a dedicated sensor, most automotive manufacturers have relied on an estimate of the oil temperature in order to save the cost of the sensor. For example, the oil temperature can be estimated based on the engine coolant temperature or inferred based on various engine response time measurements. However, these techniques typically require extensive calibration effort, and often provide only a rough estimate of the oil temperature. Accordingly, what is needed is an estimation method for use in production applications that is simple to implement and that provides a more accurate estimation of the engine oil temperature.
The present invention is directed to an improved method of estimating the crankcase oil temperature of an internal combustion engine by modeling the net heat flow through the oil during operation of the engine based on known engine operating parameters and integrating the net heat flow to update the oil temperature estimate. The net heat flow components include heat added to the oil due to fuel combustion and heat rejected from the oil to the engine coolant and atmospheric air, and are based on heat transfer coefficients that are adjusted to take into account variations in engine speed, vehicle speed and cooling fan operation.